PROJECT SUMMARY As the US population ages, the number of people living with Alzheimer?s Disease and related dementias (ADRD) is projected to triple by 2050. Although the life expectancy of American Indian and Alaska Natives (AI/ANs) is much shorter than that of other US populations, it has dramatically increased in the last few decades, with the expansion of the AI/AN elder population expected to continue. Compared to most US populations, AI/ANs bear a disproportionate burden of many established modifiable risk factors for dementia, such as diabetes, obesity, and smoking. However, our knowledge about dementia in this population remains to be severely limited. So far, only a handful of studies have examined dementia among AI/ANs, with reliable data on the prevalence or incidence of dementia in this population being nonexistent. Given so many gaps in our knowledge about dementia among AI/ANs, a systematic investigation is urgently needed to identify how problematic dementia is in this population and its impact on the Indian health system to enable more precise planning and prioritization of resources needed to support relevant health care policy. Here, leveraging on 16 years of longitudinal data available in the Indian Health Service (IHS) Data Project, a synthesis of existing IHS electronic health data for nearly 30% of the IHS service population (~ 640,000 AI/ANs), we propose to address 4 major knowledge gaps about dementia among AI/ANs as guided by the following specific aims: (1) Estimate dementia prevalence, incidence, and comorbidity rates among AI/AN elders by individual and community characteristics, such as age, gender, location, and county level socioeconomic status; (2) Characterize the association between dementia and potentially modifiable risk factors, such as diabetes, obesity, tobacco use, binge drinking, traumatic brain injuries and depression; (3) Evaluate the influence of dementia and comorbidity status on health service utilization patterns, including inpatient, outpatient, and pharmacy services; and (4) Examine the costs of providing treatment among AI/ANs with dementia, and factors that influence these costs such as comorbidity status. Our proposed analyses will provide a relatively accurate and complete picture for the epidemiology of diagnosed dementia among AI/ANs based on a large and geographically diverse sample, and contribute to the understanding of dementia and associated health service utilization in an extremely underserved population living in disadvantaged communities. Our findings promise to lay groundwork for future studies on dementia to address both the needs of AI/ANs and those of other similarly underserved populations.